Metal tubes having a through-hole formed in the center are used, for instance, as fixing tubes in laser beam printers and the like. The fixing tube varies in its manner of use depending on whether it is used in monochrome copiers, color copiers, color printers or the like. In a widely employed method in monochrome copiers, for instance, images, characters and so forth are fixed by fixing toner onto paper by way of a heated roller (fixing roller). The fixing roller for carrying out such fixing is ordinarily a thin-walled metal tube, the surface of which is covered or coated with a fluororesin.
Disclosed methods for manufacturing metal tubes involve plastic working of a metal sheet. The applicants have proposed a plastic working technology for metal tubes in which a thin-walled metal tubular body is processed by plastic working, specifically by spinning (for instance, Japanese Patent Application Laid-open No. 2004-174555; Patent document 1). A thinner-walled tube is advantageous in that preheating of the tube takes less time when the tube used, for instance, as a fixing roller of a copier. In this regard, therefore, the tube is preferably as thin as possible, so long as the necessary mechanical strength is not impaired thereby. In a tube-making technology in which a metal tube is covered with a fluororesin, a fluorine tube for fixing members has also been proposed in which axial shrinkage ranges from 1 to 8% and radial shrinkage ranges from 2 to 8% upon heating at 150° C.
The fixing tube manufactured in accordance with the present invention is ordinarily used, for example, in a copier, as follows. An image is exposed on a photosensitive drum whose surface electric resistance changes when irradiated with light, to form an electrostatic latent image on the drum. Toner, which is a magnetic powdery ink, is caused to adhere to the electrostatic latent image, to yield an image having toner adhering thereonto. The image with toner adhering thereonto is transferred to paper.
In transfer, the back of the paper is imparted positive charge by a transfer roller, whereupon the toner on the surface of the photosensitive drum is transferred to the paper. After transfer, the paper is separated from the photosensitive drum and the image having that transferred toner adhering thereon in an unfixed state is heated by a fixing tube (fixing roller) to soften the toner. The toner is fixed by pressing, to complete image copying. The method for manufacturing a tube according to the present invention is a method for manufacturing a tube for a roller, for instance, a fixing roller used in the above copying process.
It is required that the transfer rollers, fixing rollers and the like have better performance in terms of, for instance, facilitating separation between paper and rollers after transfer and fixing under high speed operation and ensuring reliable fixing, taking deformation during use of a copier in consideration.
Conventional processing methods, however, do not contemplate a process of forming a below-described spiral pattern on the outer peripheral face of the metal tube. No technologies have been disclosed in which a spiral pattern can be imparted to a thin-walled metal tube during ordinary working, without subjecting the metal tube to a supplementary process.
As described above, a fixing roller is formed by covering a metal tube with a resin as a coating material. The surface of the fixing roller is deformed readily, through expansion and contraction, when heated during use, particularly in the case of thin-walled rollers. Such fixing rollers are exposed to harsh conditions in use, for instance by heating, and yet must be durable, while problems such as deformation of fixing roller and peeling of the coating material should not occur no matter how harsh the conditions in use may be. In other words, the coating material must cover the metal tube securely.
In general, the coating depends on the shape of the metal tube. Specifically, a concave surface on the outer periphery of the metal tube results in a concave shape in the finished article after coating, while a convex surface of the metal tube results in a convex shape in the finished article after coating. When the metal tube is thin-walled, however, it is difficult to preserve at all times, for example, concave shape of the surface of the metal tube.
The above conventional technologies were problematic, in particular, as regards mass production of stable articles. Ideally, the outer peripheral face and/or inner peripheral face of the metal tube should be shaped as having fine irregularities at a fixed interval, i.e. should be shaped in a spiral pattern, regardless of the thinness of the metal tube wall. Development of such a tube and of a method for manufacturing such a tube has been desired.